Ulla Freyschuss

Sinus arrhythmia in man: influence of tidal volume and oesophageal pressure.

The effect of tidal volume (VT) and of the intrathoracic pressure (Poes) on the respiratory sinus arrhythmia (RSA) was studied in healthy subjects. They breathed into a spirometer with a VT of 1, 1.5, and 2 1, at a standardized, slow respiratory rate, 6-min-1 (A). Poes was varied by (B) adding a negative inspiratory pressure (NIP) of 5 cm of water and by (C) intermittent positive pressure ventilation (IPPV) at identical VT and respiratory frequency. In a separate study (D), intermittent negative pressure ventilation (INPV) was induced by applying negative pressure on the thorax. In A, increasing VT provoked an augmented RSA by a more marked tachycardia as well as bradycardia. On increasing the amplitude of Poes in B, RSA was somewhat more marked due to a lower minimum heart rate. When comparing respiratory cycles that had similar Poes but a different VT, the larger VT caused a slight increase in the RSA amplitude due to a more marked deceleration of the heart rate. IPPV almost abolished RSA, whereas INPV did not reduce the arrhythmia. It is concluded that pulmonary stretch reflexes to a minor extent contribute to RSA, whereas the hypothesis of a central nervous origin does not gain support. Cardiovascular reflexes remain the main possible cause of RSA.

Exercise energy expenditure in extreme obesity: influence of ergometry type and weight loss

Bicycle and treadmill exercise tests including oxygen uptake (VO2) and heart rate (HR) determination were carried out on a total of thirty patients with obesity, seventeen of whom were reinvestigated after weight loss. During both types of work VO2 for a given load was higher when compared to healthy controls. The increase of VO2 was more marked when cycling was performed in sitting position than in supine. The mechanical efficiency of sitting bicycle exercise averaged 17.8% and was negatively related to the percentage overweight; the slope of the VO2/load regression line was slightly less in comparison to the controls, while no such difference was found during treadmill walking. After weight reduction the VO2/load regression line was skifted downwards, the slopes being unchanged, thus the mechanical efficiency improved. This study not only confirms the observation of a low mechanical efficiency of obese subjects but also demonstrates that the change is quantitatively related to the overweight. The lowered efficiency was caused by body mechanical factors and there was no support for an abnormal muscular efficiency. Exercise tests should be combined with VO2 determination, if used to assess the circulatory capacity of obese subjects.

Respiratory Sinus Arrhythmia in Man: Relation to Cardiovascular Pressures

The relationship of respiratory sinus arrhythmia (RSA) to the accompanying oscillations of cardiovascular pressure has been studied in five healthy subjects. Tidal volume (VT) of 1.0, 1.5, and 2.0 1 at the breathing rate of 6 c-min-1 were used as reference. With identical VT oesophageal pressure was varied by negative inspiratory pressure (NIP) and intermittent positive-pressure ventilation (IPPV). Compared with control, NIP with 1.01 significantly increased RSA, the oscillations of brachial artery pressures (PBA), and the net filling pressures of the ventricles. IPPV did not significantly change the variations of PBA but reduced RSA and the respiratory variations of the right ventricular end-diastolic net pressure. During control breathing and with NIP the acceleration of heart rate during inspiration was associated with rising PBA and rising net filling pressures of both ventricles. The results indicate that RSA may be elicited by cardiovascular reflexes due to changes in venous filling of the heart rather than by the variations in systemic arterial pressure.

Circulatory and respiratory adaptation in man to acute withdrawal and reinfusion of blood

SummaryIn eight healthy men 950 g of blood (12.2–17.6% of the blood volume) was withdrawn and reinfused after about half an hour. Respiration and circulation were studied by analyses of expiratory gas, blood gases and data from right heart catheterization. On hemorrhage oxygen uptake and cardiac output decreased by 10 and 28%, respectively; both varied indirectly with the blood loss. The pressures in the right ventricle, pulmonary and systemic arteries fell without relation to the cardiac output. Mean heart rate did not change significantly, but a moderate positive covariation (P<0.05) between heart rate and arterial blood pressure was found during bleeding. This result was confirmed by the relative bradycardia noted in the period prior to reinfusion. On refilling of the blood the oxygen uptake and the pulmonary arterial pressures increased above the initial value. The heart rate varied directly with the arterial pressure also during reinfusion. The observations demonstrate a depression of the metabolism and circulation on moderate hemorrhage. Part of these effects is tentatively referred to a lowered set point of the arterial baroreflexes.

Comparison between Arm and Leg Exercise in Women and Men

Arm and leg work was performed on bicycle ergometers in sitting position by fourteen women and sixteen men. Heart rate, minute volume of ventilation (VE), and oxygen consumption (VO2) were measured. Arm exercise was performed until (muscular) exhaustion, leg exercise up to a heart rate of circa 170 beats/min. At comparable work loads arm exercise evoked higher VO2, VE, and heart rate than leg exercise irrespective of sex. At comparable VO2, the heart rate and VE were higher during arm work in both sexes, VE more so among the men. With the same limbs working, the mechanical efficiency was equal in both sexes. The regression coefficients of heart rate on load or VO2 was higher for the women irrespective of work type. A close correlation was obtained between working capacity at a heart rate of 170 beats/min (W170) during leg and arm exercise and between W170 of leg exercise and W150, similarly calculated during arm work. Thus W170 of leg exercise could be calculated from either a maximal or submaximal arm work.

Effects of withdrawal and reinfusion of blood on limb circulation at rest and during contralateral isometric handgrip.

An isometric handgrip induces a rapid decrease in vascular resistance in the resting contralateral forearm presumably mainly mediated by β-adrenergic effects. This response was used to elucidate if a moderate blood loss provokes an altered peripheral vascular reactivity. Thus, heart rate, arterial pressures and forearm and calf blood flow were studied in eight healthy males at rest, and during contralateral isometric handgrip (CIH) before and after withdrawal of about 16% of the blood volume and again after reinfusion. Resting values of cardiac output, right atrial and pulmonary arterial pressures were also measured. Blood withdrawal reduced stroke volume and cardiac output by one fifth and slightly decreased arterial pressure compared to control state, thus total systemic resistance was increased. Mean forearm and calf blood flows were not significantly changed although forearm vascular resistance increased moderately. The response to CIH of heart rate and arterial mean pressure was similar in the normov...

Respiratory Sinus Arrhythmia in Man: Relation to Right Ventricular Output

The respiratory effects on heart rate (HR), right ventricular stroke volume (SV RV) and the pulmonary arterial flow (PAF) have been studied beat-by-beat in seven conscious, healthy subjects. Tidal volumes (VT) of 1.0 and 2.0 liters at a breathing rate of 6 c x min-1 were used as controls. With identical VT and respiratory rate intrathoracic was affected by (A) negative inspiratory pressure (NIP) of 5 cm of water and (B) with intermittent positive pressure ventilation (IPPV). In the control experiments all subjects exhibited an inspiratory increase in HR (respiratory sinus arrhythmia) as well as in SV RV. With VT of 1.0 liter, NIP augmented the inspiratory increase in SV RV and the respiratory oscillations of PAF. IPPV decreased SV RV and HR during inspiration. It is concluded that NIP and IPPV affect the SV RV and the right heart blood flow. The similar effects on HR and SV RV suggest a causal relationship which might be explained by heart rate regulating reflexes from the heart.

Effect of acute blood volume variations in man on the circulatory response to isometric handgrip

In normovolaemia (NV) a strong muscle activation performed as an isometric handgrip induced an initial transient decrease in vascular resistance in the resting forearm, probably mediated partly by β-adrenergic mechanisms. In hypovolaemia (HV) this reaction was less pronounced. To elucidate if the altered peripheral reaction to a contralateral isometric handgrip (CIH) could be explained by an altered response of the central circulation, the peripheral and central circulatory response to CIH was studied in eight healthy males after withdrawal and reinfusion of approximately 16% of the blood volume. The effects of blood loss at rest were the same as previously reported except for the fact that arterial pressures were not significantly lowered. During CIH in NV heart rate, cardiac output, arterial and pulmonary pressures and total systemic vascular resistance (TSR) increased and stroke volume decreased. The forearm vascular resistance fell. In HV, CIH induced the same changes in cardiac output, heart rate, st...

Selected Papers on Lipid Metabolism

In patients with various manifestations of atherosclerotic vascular disease, hypertriglyceridemia is very common To determine whether the hypertriglyceridemia is caused by an increased influx or decreased removal of plasma TG requires a reliable method for estimating plasma TG turnover rate [197]. This study deals with the evaluation of such methods.